Genetic analysis of sinonasal undifferentiated carcinoma discovers recurrent SWI/SNF alterations and a novel PGAP3-SRPK1 fusion gene.

BACKGROUND: Sinonasal Undifferentiated Carcinoma (SNUC) is a rare and aggressive skull base tumor with poor survival and limited treatment options. To date, targeted sequencing studies have identified IDH2 and SMARCB1 as potential driver alterations, but the molecular alterations found in SMARCB1 wild type tumors are unknown. METHODS: We evaluated survival outcomes in a cohort of 46 SNUC patients treated at an NCI designated cancer center and identify clinical and disease variables associated with survival on Kaplan-Meier and Cox multivariate survival analysis. We performed exome sequencing to characterize a series of SNUC tumors (n = 5) and cell line (MDA8788-6) to identify high confidence mutations, copy number alterations, microsatellite instability, and fusions. Knockdown studies using siRNA were utilized for validation of a novel PGAP3-SRPK1 gene fusion. RESULTS: Overall survival analysis revealed no significant difference in outcomes between patients treated with surgery +/- CRT and CRT alone. Tobacco use was the only significant predictor of survival. We also confirmed previously published findings on IDH and SMARC family mutations and identified novel recurrent aberrations in the JAK/STAT and PI3K pathways. We also validated a novel PGAP3-SRPK1 gene fusion in the SNUC cell line, and show that knockdown of the fusion is negatively associated with EGFR, E2F and MYC signaling. CONCLUSION: Collectively, these data demonstrate recurrent alterations in the SWI/SNF family as well as IDH, JAK/STAT, and PI3K pathways and discover a novel fusion gene (PGAP3-SRPK1). These data aim to improve understanding of possible driver mutations and guide future therapeutic strategies for this disease.

Lip and Perioral Trauma: Principles of Aesthetic and Functional Reconstruction.

Successful management of lip and perioral trauma requires a nuanced understanding of anatomy and surgical techniques. Surgical correction is particularly challenging in instances of tissue loss, due to a narrow tolerance for aesthetic deformity and highly specialized functions of the perioral region, including facial expression, communication, and oral competence. Restoring continuity of the orbicularis oris musculature is critical for dynamic sphincter function of the upper and lower lips. Lip and perioral tissue symmetry are also critical for aesthetic balance, and failure to restore a natural appearance can adversely affect personal identity, with attendant psychological trauma. This discussion of lip and perioral trauma management encompasses lip and perioral anatomy, evaluation of injuries, reconstructive techniques, and prevention and management of complications. Perioral injuries are classified by size, depth, and extent of injury, and the corresponding reconstructive approaches are a function of complexity. These approaches proceed sequentially up rungs of the reconstructive ladder including primary repair, local flaps, grafting, regional flaps, as well as microvascular free tissue transfers. Procedures may be single stage or require multiple stages or subsequent refinement. Regardless of the defect size or location, the guiding principle of repair in the perioral region is restoring natural function and aesthetic appearance. This still-evolving area of facial plastic and reconstructive surgery lends itself to artistry and technical precision, offering opportunities for further innovation to improve the outcomes of patients with lip and perioral trauma.

Predictors of survival in patients undergoing oropharyngeal surgery for cancer recurrence after radiation therapy.

PURPOSE: The incidence of oropharyngeal squamous cell carcinoma continues to rise with the majority of patients receiving definitive or adjunctive radiation. For patients with locoregional recurrence after radiation, optimal treatment involves salvage surgery. The aim of this study is to identify factors that predict survival to ultimately improve patient selection for salvage surgery. METHODS: Retrospective cohort study at an NCI-designated cancer center. We analyzed patients with a history of head and neck radiation who presented with persistent/recurrent or second primary disease requiring salvage oropharyngeal resection from 1998-2017 (n = 120). Patients were stratified into three classes based on time to recurrence and presence of laryngopharyngeal dysfunction. Primary outcomes were 5-year overall survival (OS) and disease specific survival (DSS). RESULTS: Median OS was 27 months (median follow-up 20 months). Five-year OS was 47% for class I (recurrence > 2 years), 26% for class II (recurrence ≤ 2 years), and 0% for class III (recurrence ≤ 2 years and laryngopharyngeal dysfunction), (p < 0.0001). Five-year DSS showed significant differences between classes (p < 0.0001). On multivariate analysis, class remained predictive of OS (p = 0.04- < 0.001) and DSS (p = 0.04-0.001). Adjuvant radiation after salvage surgery with negative margins showed superior OS (71% vs. 28%, p = 0.01) and DSS (83% vs 37%, p = 0.02) compared to surgery alone and was a significant predictor of improved survival on multivariate analysis (HR 0.1, p = 0.04). CONCLUSION: This study identified a subset of patients with oropharyngeal cancer recurrence within two years of initial treatment and with laryngopharyngeal dysfunction who have poor outcomes for salvage surgery.

Use of the spider limb positioner for fibular free flap reconstruction of head and neck bony defects.

BACKGROUND: Osseous and osteocutaneous fibular free flaps are the workhorse of maxillomandibular reconstruction over 30 years after the initial description. Since 2019, we have routinely used the Spider Limb Positioner, adapted from its use in shoulder orthopedic procedures, for fibular free flap harvest. Herein, we describe this novel technique in our cohort. METHODS: We describe our intraoperative setup and endorse the versatility and utility of this technique in comparison to other reported fibular free flap harvest techniques. RESULTS: The Spider Limb Positioner was used 61 times in 60 different patients to harvest osseous or osteocutaneous fibular free flaps. Median (range) tourniquet time for flap harvest was 90 (40-124) minutes. No iatrogenic nerve compression injuries or complications related to lower extremity positioning occurred. CONCLUSION: We describe a novel approach to fibular free flap harvest utilizing the Spider Limb Positioner, which affords optimal ergonomics, visibility, and patient repositioning. There were no nerve injuries or complications related to positioning in our series.

Association of preoperative thyroid hormone replacement with perioperative complications after major abdominal surgery.

OBJECTIVE: To determine the association between preoperative thyroid hormone replacement and complications following major abdominal surgery. METHODS: A retrospective case series was performed of patients enrolled in the Michigan Surgical Quality Collaborative (MSQC) who underwent major abdominal surgery at an academic institution over a 10-year period. The principal explanatory variable was preoperative thyroid hormone replacement. Primary outcomes were morbidity, mortality and length of stay. RESULTS: 2700 patients were identified. On multivariate analysis correcting for established predictors of operative morbidity, patients on preoperative thyroid replacement had a 1.5- fold increased risk of serious morbidity(p â€‹= â€‹0.01), and a 1.7- fold greater risk for serious sepsis(p â€‹= â€‹0.04). Thyroid replacement was associated with longer length of stay(p â€‹< â€‹0.001). While there was a high degree of missing data for surgical approach (31.1 â€‹% missing data), results suggest that patients on thyroid hormone replacement were more likely to undergo an open rather than minimally invasive surgery(p â€‹< â€‹0.01). Open surgery was associated with greater risk of serious morbidity(p â€‹= â€‹0.003) and longer length of stay(p â€‹< â€‹0.001). CONCLUSIONS: Preoperative thyroid hormone replacement independently predicts operative morbidity and length of stay following major abdominal surgery.

Pharyngeal Mucosal Margin Vessel Counts Predict Pharyngocutaneous Fistula in Salvage Laryngectomy.

OBJECTIVE: We evaluated vessel counts in the pharyngeal mucosal margins of patients who underwent salvage laryngectomy to establish whether mucosal vascularity might predict fistula risk. STUDY DESIGN: Retrospective cohort. SETTING: Tertiary Medical Center. METHODS: Patients who underwent salvage total laryngectomy at our institution between 1999 and 2015 were identified. Pharyngeal mucosal margins from laryngectomy specimens were evaluated histologically for each patient, and vessel counts were performed on 5 ×10 images. The primary outcome measure was fistula within 30 days of surgery and mean vessel counts were assessed as the principle explanatory variable. RESULTS: Seventy patients were included and 40% developed a postoperative fistula. There was a large difference in the mean vessel count in patients who did develop fistula (48.6 vessels/×10 field) compared to those who did not (34.7 vessels/×10 field). A receiver operative characteristic curve found that a cutoff value of 33.9 vessels/×10 field provided a sensitivity of 75% and specificity of 62% to predict the likelihood of fistula occurrence (area under the curve = 0.71, 95% confidence interval [CI]: 0.59-0.83). In a binary logistic regression, patients with vessel counts greater than 33.9 had a 5-fold increased risk of developing fistula (95% CI: 1.8-16.45). Histologically, vessels in the pharyngeal mucosa of patients who developed fistulas were more disorganized. CONCLUSION: After salvage laryngectomy, patients with higher mean mucosal margin vessel counts are at increased risk of fistula. The mechanism is unknown, but the disorganization of the vasculature may contribute to poor wound healing. Vessel counting may allow for fistula risk stratification and guide postoperative care.

Utility of bioselection with neoadjuvant chemotherapy for organ preservation in patients with T4 laryngeal cancer.

BACKGROUND: Neoadjuvant chemotherapy for induction selection of definitive treatment (IS) protocols have shown excellent outcomes for organ preservation and survival in patients with T3 laryngeal squamous cell carcinoma (LSCC). We seek to evaluate survival and organ preservation outcomes in T4 LSCC patients treated with IS protocols. METHODS: Retrospective cohort of advanced T3 and T4 LSCC patients who underwent IS protocols based upon potential for preserving a functional larynx. Patients received one neoadjuvant cycle of platinum-based chemotherapy with either 5-fluorouracil or docetaxel or with two cycles of platinum-based chemotherapy with docetaxel and a Bcl-2 inhibitor. Patients who achieved ≥ 50 % response as determined by radiographic review and/or endoscopic evaluation received definitive chemoradiation. Patients who had < 50 % response after IS underwent total laryngectomy (TL) followed by post-operative radiation +/- chemotherapy. RESULTS: Amongst T4 patients, 114 met inclusion criteria including 89 who underwent IS protocols and 25 who received an upfront TL. In total, 76.0 % of T3 patients and 71.9 % of T4 patients responded to IS and underwent definitive chemoradiation. There was no significant difference in hazard of death between T4 IS and T4 TL patients (HR: 0.9, p = 0.86). Among responders, there was no significant difference in 5-year laryngectomy-free survival (T3 - 59.6 %, T4 44.3 %, p = 0.15) or laryngeal preservation by T stage (T3 - 72.8 %, T4 - 73.0 %, p = 0.84). CONCLUSIONS: Select T4 patients may benefit from organ preservation using IS protocols with similar response rates to patients with T3 tumors, without compromising survival when compared to upfront TL.

Phase II Clinical Trial of Intravenous Levothyroxine to Mitigate Pharyngocutaneous Fistula in Euthyroid Patients Undergoing Salvage Laryngectomy.

PURPOSE: Patients undergoing head and neck cancer surgery after prior radiation or chemoradiation are at high risk for wound complications. Hypothyroidism is a known risk factor for wound complications, especially fistulae after salvage total laryngectomy. The purpose of this phase II clinical trial is to investigate the effect of peri-operative intravenous levothyroxine supplementation on wound complications in patients undergoing salvage total laryngectomy. PATIENTS AND METHODS: Euthyroid patients previously treated with radiation/chemoradiation undergoing total laryngectomy were prospectively recruited (n=72). Post-operatively, intravenous levothyroxine was administered at a weight-based dose (1.3 mcg/kg/day) and transitioned to enteral dosing on day 7. Free T3, T4, and thyroid stimulating hormone (TSH) were collected and dosing was adjusted accordingly. The primary endpoints were rates of fistula and fistula requiring re-operation, compared to matched historical controls. All patients were monitored for adverse effects. RESULTS: The rate of post-operative hypothyroidism was 21% compared to 49% in a matched historic cohort. The rate of fistula was 18.1% while the rate of fistula requiring re-operation was 4.2%, significantly lower than rates in our historic cohort (34.6% and 14.8% respectively, p=0.02 and 0.01). Post-operative hypothyroidism and recurrent clinical stage predicted fistula requiring re-operation in multivariate analysis; other acute phase reactants were not predictive. There were no observed adverse events related to levothyroxine supplementation. CONCLUSIONS: Post-operative intravenous levothyroxine supplementation reduced rates of acute hypothyroidism, fistula, and fistula requiring re-operation in patients undergoing salvage total laryngectomy without adverse effects. Intravenous levothyroxine is a viable strategy to reduce wound complications in this high-risk patient population.

Upfront Neck Dissection for Treatment Selection and Improvement in Quality of Life as a Novel Treatment Paradigm for Deintensification in HPV+ OPSCC.

PURPOSE: Locoregionally advanced HPV+ oropharyngeal squamous cell carcinoma (OPSCC) has excellent cure rates, although current treatment regimens are accompanied by acute and long-term toxicities. We designed a phase II deescalation trial for patients with HPV+ OPSCC to evaluate the feasibility of an upfront neck dissection to individualize definitive treatment selection to improve the quality of life without compromising survival. PATIENTS AND METHODS: Patients with T1-3, N0-2 HPV+ OPSCC underwent an upfront neck dissection with primary tumor biopsy. Arm A included patients with a single lymph node less than six centimeters, with no extracapsular spread (ECS) and no primary site adverse features underwent transoral surgery. Arm B included patients who had two or more positive lymph nodes with no ECS, or those with primary site adverse features were treated with radiation alone. Arm C included patients who had ECS in any lymph node and were treated with chemoradiation. The primary endpoint was quality of life at 1 year compared with a matched historical control. RESULTS: Thirty-four patients were enrolled and underwent selective neck dissection. On the basis of pathologic characteristics, 14 patients were assigned to arm A, 10 patients to arm B, and 9 to arm C. A significant improvement was observed in Head and Neck Quality of Life (HNQOL) compared with historical controls (-2.6 vs. -11.9, P = 0.034). With a median follow-up of 37 months, the 3-year overall survival was 100% and estimated 3-year estimated progression-free survival was 96% [95% confidence interval (CI), 76%-99%]. CONCLUSIONS: A neck dissection-driven treatment paradigm warrants further research as a deintensification strategy.

Prognosis to Radiation Unlocked: How Hypoxia Methylome May Hold the Key in HNSCC.

Hypoxia in head and neck tumors has proven to be predictive of outcomes. Current hypoxia signatures have failed for patient treatment selection. In a recent study, the authors identified a hypoxia methylation signature as a more robust biomarker in head and neck squamous cell carcinoma and shed light into the mechanism of hypoxia-mediated treatment resistance. See related article by Tawk et al., p. 3051.

Circulating Tumor DNA in Human Papillomavirus-Mediated Oropharynx Cancer: Leveraging Early Data to Inform Future Directions.

ABSTRACT: Circulating tumor DNA (ctDNA) has become an area of intense study in many solid malignancies including head and neck cancer. This is of particular interest for human papillomavirus-mediated oropharyngeal squamous cell carcinoma as this cohort of patients has excellent survival and is undergoing current clinical trials aimed at treatment de-escalation. Recent studies have demonstrated the prognostic implications of pretreatment ctDNA and the utility of monitoring ctDNA during and posttreatment; however, there is a need for a more critical understanding of ctDNA as it is beginning to be incorporated into clinical trials. This review discusses the current state of ctDNA in oropharynx cancer focusing on ctDNA kinetics and minimal residual disease detection and ends with a discussion of future applications.

Epithelial-Mesenchymal Plasticity in Tumor Immune Evasion.

Epithelial-mesenchymal transition (EMT) is a fundamental process that occurs during embryogenesis and tissue repair. However, EMT can be hijacked by malignant cells, where it may promote immune evasion and metastasis. Classically considered a dichotomous transition, EMT in cancer has recently been considered a plastic process whereby malignant cells display and interconvert among hybrid epithelial/mesenchymal (E/M) states. Epithelial-mesenchymal plasticity (EMP) and associated hybrid E/M states are divergent from classical EMT, with unique immunomodulatory effects. Here, we review recent insights into the EMP-immune cross-talk, highlighting possible mechanisms of immune evasion conferred by hybrid E/M states and roles of immune cells in EMP.

Advancement of PI3 Kinase Inhibitor Combination Therapies for PI3K-Aberrant Chordoma.

Objectives Targeted inhibitors of the PI3 kinase (PI3K) pathway have shown promising but incomplete antitumor activity in preclinical chordoma models. The aim of this study is to advance methodology for a high-throughput drug screen using chordoma models to identify new combination therapies for chordoma. Study Design Present work is an in vitro study. Setting The study conducted at an academic research laboratory. Materials and Methods An in vitro study on automated high-throughput screening of chordoma cells was performed using a library of 1,406 drugs as both mono- and combination therapies with PI3K inhibitors. Combination indices were determined for dual therapies and synergistic outliers were identified as potential therapeutic agents. T (brachyury) siRNA knockdown in combination with PI3K pathway inhibition was also assessed. Results Fifty-nine combination therapies were identified as having potential therapeutic efficacy. Effective combinations included PI3K inhibitors with GSK1838705A (ALK/IGF-1R inhibitor), LY2874455 (VEGFR/FGFR inhibitor), El1 (selective Ezh2 inhibitor), and (-)-p-bromotetramisole oxalate (alkaline phosphatase inhibitor). The top ranking targets identified included ALK, PDGFR, VEGFR, aurora kinase, and BCL-2. T (brachyury) inhibition produced significant reduction in cell viability and growth; however PI3K inhibition in combination with T (brachyury) knockdown did not result in further reduction in growth and viability in vitro. Conclusion High throughput with in vitro combination screening is feasible with chordoma cells and allows for rapid identification of synergistic dual-therapies. Potential combination therapies and targetable pathways were identified. T (brachyury) knockdown produced significant reduction in cell viability, but did not show additional benefit with PI3K pathway inhibition in this model. Further in vitro and in vivo validation of these therapeutic combinations is warranted.

Analysis of Human Papilloma Virus Content and Integration in Mucoepidermoid Carcinoma.

Mucoepidermoid Carcinomas (MEC) represent the most common malignancies of salivary glands. Approximately 50% of all MEC cases are known to harbor CRTC1/3-MAML2 gene fusions, but the additional molecular drivers remain largely uncharacterized. Here, we sought to resolve controversy around the role of human papillomavirus (HPV) as a potential driver of mucoepidermoid carcinoma. Bioinformatics analysis was performed on 48 MEC transcriptomes. Subsequent targeted capture DNA sequencing was used to annotate HPV content and integration status in the host genome. HPV of any type was only identified in 1/48 (2%) of the MEC transcriptomes analyzed. Importantly, the one HPV16+ tumor expressed high levels of p16, had high expression of HPV16 oncogenes E6 and E7, and displayed a complex integration pattern that included breakpoints into 13 host genes including PIK3AP1, HIPI, OLFM4,SIRT1, ARAP2, TMEM161B-AS1, and EPS15L1 as well as 9 non-genic regions. In this cohort, HPV is a rare driver of MEC but may have a substantial etiologic role in cases that harbor the virus. Genetic mechanisms of host genome integration are similar to those observed in other head and neck cancers.

Tumor-Infiltrating Lymphocytes in Patients With Advanced Laryngeal Cancer Undergoing Bioselection.

OBJECTIVE: Bioselection to assess tumor response after induction chemotherapy has been introduced as an alternative treatment strategy to total laryngectomy for patients with advanced larynx squamous cell carcinoma (LSCC). Tumor-infiltrating lymphocytes (TILs) have proven to serve as prognostic biomarkers in head and neck cancer but have not been evaluated as a way to select patients for treatment paradigms. The aim of this study is to evaluate the role of pretreatment TILs in patients with advanced LSCC undergoing the bioselection paradigm. STUDY DESIGN: Retrospective study. SETTING: Tertiary care hospital. METHODS: Patients with advanced LSCC treated with bioselection and available tissue were included (N = 76). Patients were stratified into CD8-low and CD8-high cohorts by using the median TIL count. Kaplan-Meier survival analysis and multivariate cox regression were performed with SPSS version 26 (IBM). RESULTS: After controlling for tobacco use, tumor site, and stage, a high CD8 TIL count was an independent predictor of improved 5-year disease-specific survival (hazard ratio, 0.17 [95% CI, 0.03-0.84]; P = .03). CD8 TIL counts did not predict response to induction chemotherapy; however, subgroup analysis of patients treated with chemoradiation therapy revealed that CD8 TIL count was significantly associated with degree of response (P = .012). CONCLUSION: These findings support prior data published by our group showing that TILs are predictive of disease-specific survival in patients with head and neck cancer. CD8 TIL counts were significantly associated with degree of clinical response after induction chemotherapy. These results suggest that pretreatment assessment of tumor-infiltrating CD8 cells could be useful in selecting patients.

Early HPV ctDNA Kinetics and Imaging Biomarkers Predict Therapeutic Response in p16+ Oropharyngeal Squamous Cell Carcinoma.

PURPOSE: In locally advanced p16+ oropharyngeal squamous cell carcinoma (OPSCC), (i) to investigate kinetics of human papillomavirus (HPV) circulating tumor DNA (ctDNA) and association with tumor progression after chemoradiation, and (ii) to compare the predictive value of ctDNA to imaging biomarkers of MRI and FDG-PET. EXPERIMENTAL DESIGN: Serial blood samples were collected from patients with AJCC8 stage III OPSCC (n = 34) enrolled on a randomized trial: pretreatment; during chemoradiation at weeks 2, 4, and 7; and posttreatment. All patients also had dynamic-contrast-enhanced and diffusion-weighted MRI, as well as FDG-PET scans pre-chemoradiation and week 2 during chemoradiation. ctDNA values were analyzed for prediction of freedom from progression (FFP), and correlations with aggressive tumor subvolumes with low blood volume (TVLBV) and low apparent diffusion coefficient (TVLADC), and metabolic tumor volume (MTV) using Cox proportional hazards model and Spearman rank correlation. RESULTS: Low pretreatment ctDNA and an early increase in ctDNA at week 2 compared with baseline were significantly associated with superior FFP (P < 0.02 and P < 0.05, respectively). At week 4 or 7, neither ctDNA counts nor clearance were significantly predictive of progression (P = 0.8). Pretreatment ctDNA values were significantly correlated with nodal TVLBV, TVLADC, and MTV pre-chemoradiation (P < 0.03), while the ctDNA values at week 2 were correlated with these imaging metrics in primary tumor. Multivariate analysis showed that ctDNA and the imaging metrics performed comparably to predict FFP. CONCLUSIONS: Early ctDNA kinetics during definitive chemoradiation may predict therapy response in stage III OPSCC.

Prognostic value of CD103+ tumor-infiltrating lymphocytes and programmed death ligand-1 (PD-L1) combined positive score in recurrent laryngeal squamous cell carcinoma.

OBJECTIVES: In an evolving era of immunotherapeutic options for persistent or recurrent laryngeal squamous cell carcinoma (LSCC), there is a need for improved biomarkers of treatment response and survival to inform optimal treatment selection and prognostication. Herein, our primary objective was to explore correlations between tumor infiltrating lymphocytes (TILs) and PD-L1 Combined Positive Score (CPS). Secondarily, we sought to explore their combined association with survival outcomes in patients with persistent or recurrent LSCC treated with salvage surgery. MATERIALS AND METHODS: This was a retrospective cohort study at a single academic medical center. Immunohistochemistry staining for TILs and PD-L1 was performed on a tissue microarray of persistent or recurrent LSCC pathologic specimens. Correlations between TIL subsets and PD-L1 CPS were examined using Pearson's correlation coefficient and survival outcomes were analyzed with the Kaplan-Meier method and log-rank tests. RESULTS: Only CD103+ TILs showed a statistically significant, weakly-positive correlation with PD-L1 CPS (r2 = 0.264, p < 0.015). No other TIL subsets correlated with PD-L1 CPS in our cohort. The most favorable survival outcomes were seen in patients with pathologic N0 tumors showing high CD103+ TILs and/or high PD-L1 CPS staining. CONCLUSION: Among patients with persistent or recurrent LSCC, CD103+ TILs only modestly correlated with PD-L1 CPS. A combined biomarker score incorporating CD103+ TILs and PD-L1 CPS greatly enhanced survival discrimination. This model may have additional utility in predicting the clinical benefit of immunotherapies in persistent or recurrent LSCC in the future.

Advancement in Cancer Stem Cell Biology and Precision Medicine-Review Article Head and Neck Cancer Stem Cell Plasticity and the Tumor Microenvironment.

Head and Neck cancer survival has continued to remain around 50% despite treatment advances. It is thought that cancer stem cells play a key role in promoting tumor heterogeneity, treatment resistance, metastasis, and recurrence in solid malignancies including head and neck cancer. Initial studies identified cancer stem cell markers including CD44 and ALDH in head and neck malignancies and found that these cells show aggressive features in both in vitro and in vivo studies. Recent evidence has now revealed a key role of the tumor microenvironment in maintaining a cancer stem cell niche and promoting cancer stem cell plasticity. There is an increasing focus on identifying and targeting the crosstalk between cancer stem cells and surrounding cells within the tumor microenvironment (TME) as new therapeutic potential, however understanding how CSC maintain a stem-like state is critical to understanding how to therapeutically alter their function. Here we review the current evidence for cancer stem cell plasticity and discuss how interactions with the TME promote the cancer stem cell niche, increase tumor heterogeneity, and play a role in treatment resistance.